Coating apparatus



Aug. 29, 1944. G. D. MUGGLETON COATING APPARATUS Filed Jan. 27, 1941 NNWRN -W v v C Raw MN mN sh I Q MN MN NW NW Patented Aug. 29, 19442,356,873 comma APPARATUS Gerald D. Muggleton, Appleton, Wis., assignorto Consolidated Water Power & Paper Company, Wisconsin Rapids, Wis., acorporation of Wisconsin Application January 27, 1941, Serial No.376,027

2 Claims.

This invention relates to improvements in means for coating paper, andrefers specifically to an apparatus for coating paper whereinunevenness, streaks, tracks or the like in the coating are preventedduring the coating operation.

In roll coating operations, that is, operations wherein a mobile coatingmaterial is applied to the surface of a web of paper or the like bymeans of an applicator or coating roll, difliculty is sometimesencountered in that streaks, ridges, tracks or the like are formed inthe coating film upon the web. These disfigurations appear to be due tothe surface tension of the mobile coating and are frequently exaggeratedby the use of binders necessary for a satisfactory coating material, andwithout which the coatings would not adhere to the web surface. Thestreaks or tracks are formed primarily when the applicator roll surfaceleaves the surface of the web after the coating has been depositedthereon and the disfiguration appears to be accentuated where theapplicator roll surface and the web surface part in a more or lessgradual manner. Where the parting of the roll surface and the coated webis more abrupt, the track formation appears to be minimized.

Briefly described, my invention contemplates the application of a fluidcoating material to a web of paper by means of a rotating surface, andimmediately following the initial application of the coating to the weba coating stripping blade strips coating from the rotating surface anddeposits it upon the web. The coating stripping blade is so constructedand so positioned that the web immediately moves between a surface ofthe blade and a second rotating surface in such a manner that thecoating film is smoothed by the blade surface.

Two important features are inherent in my invention; one, by strippingthe coating from the applicator roll a comparatively abrupt separationof the web surface from the applicator roll surface is brought about,and in addition a greater quantity of coating material can be applied tothe web surface per pass, and; two, the coating carried by the web issmoothed before the fibrous web has an opportunity to absorb the liquidportions of the coating material, that is, before the coating materialpartially sets or loses a portion of its mobility.

Other objects and advantages of my invention will be apparent from theaccompanying drawing and following detailed description.

In the drawing,

Fig. 1 is a diagrammatic view of suitable apparatus for carrying out myinvention.

Fig. 2 is an enlarged detailed view of the coating stripping blade inoperative position.

Referring in detail to the drawing, l and 2 indicate the last two drierdrums of a battery of driers which comprises the dry end of the usualpaper machine (not shown). A web of paper 3, passed from the wet end ofthe paper machine is trained around the drier drums comprising thedrying section of the machine and is passed from the last drier drum 2to a calender stack 4 which comprises a plurality of superimposed rollsbe tween which the web 3 passes and the surfaces thereof are smoothed.

After leaving the calender stack 4, the web is passed over guide rolls 5and 6 carried between rolls 1 and 8. Roll 8 is a coating roll orapplicator roll and roll I is a bed roll. Roll 8 is preferablyconstructed of metal and has a relatively highly finished surface, andthe surface of roll I is preferably constructed of rubber or otherresilient material.

A pair of osculating rolls 9 and I0, having their axes disposed insubstantially the same horizontal plane, are positioned adjacent roll 8.A dam H is positioned at each end of the nip formed by the rolls 9 andI0 and extends into said nip to prevent mobile coating material, passedto the nip through pipe l2, from leaking out at the ends of the nip.This arrangement of rolls is well known to the art and is frequentlyreferred to as a metering or gate roll arrangement. A transfer roll I3is in osculating relationship with rolls 8 and 9 and serves to conveycoating material from the surface of roll 9 to the surface of theapplicator roll 8.

As a feature of my invention, I position in the exit nip of the rolls Iand 8, a coating stripping blade H. The member I4 is supported by aportion of the frame of the machine (not shown) to which a bracket I5 isattached. The opposite end of the member [4 is brought to a relativelysharp edge, as indicated at l6 in Fig. 2. The member I4 extends thelength of th roll 8 and the edge It bears upon the surface of said roll.On one side of the edge, that is, the side adjacent the applicator roll,the member I4 is fiat, as shown at ll in Fig. 2. but on the oppositeside of the edge the member is curved in substantial conformity with thebed roll, as shown at l8 in Fig. 2.

As will be hereinafter more fully described a portion of the coatingmaterial carried upon the surface of roll 8 contacts and is depositedupon a surface of the web 3 in a manner quite similar to the operationof conventional roll coaters.

However, as the web proceeds further into the nip of rolls 1 and 8, theedge It, in contact with the surface of roll 8 strips substantially allof the coating material upon the surface of roll 8 and diverts it intocontact with the web surface. The coated web then passes between thecurved surface I8 and the surface of roll I wherein the coating issmoothed.

The web 3 after passing between the curved surface I8 and roll 1 iscarried around a heated drier drum IS. A chest 20 is positioned over thefreshly coated side of the web 3 during its travel from roll I to drumI3 and during a portion of its travel over the surface of drum l9. Airunder pressure, preferably heated air, is introduced into the chest 20through conduit 2! and the chest is provided with a plurality ofapertures 22 whereby air under pressure is blown upon the freshly coatedsurface. The combination of the heated drum l9 and the air blown uponthe freshly coated surface of the web causes the coating materialcarried by the web to set whereby said web may be trained around guiderolls 23 with the coated side in contact with the guide roll surfaceswithout marring said coated surface.

The web 3 after leaving the last guide roll 23 is carried into the nipof rolls 24 and 25, roll 24 being a, bed roll similar to roll I and roll25 being a coating or applicator roll similar to roll 8. A pair of gaterolls 26 and 21 are disposed adjacent roll 25, said gate rolls carryinga dam 28 adjacent each end of the nip formed by said rolls. Coatingmaterial is introduced into the nip of the gate rolls by means of pipe29, the arrangement being similar to that comprising rolls 9 and I0, damII and pipe l2, hereinbefore described.

a coating stripping blade I4 is positioned in t exit nip of rolls 24 and25 and functions in a manner hereinafter more fully described. The web 3after leaving the roll 24 wherein it was confined between the surface ofsaid roll and the curved surface 18 of the member H, is passed to thesurface of a drier drum 30. A chest 3| is positioned beneath the coatedsurface of the web 3 during its passage from roll 24 to drum 30 andduring a portion of its passage over the surface of said drum. The chest3| is provided with a plurality of apertures whereby air under pressure,preferably heated air, passed into the chest 3| through conduit 32, isdischarged into contact with the freshly coated surface of the web 3.The combination of the heated drum and the air discharged from the chest3| tends to set the coating on-the web and permits the web to be trainedaround the guide rolls 33 with its coated surface in contact with thesurfaces of the guide rolls.

After passing around the last guide roll 33 the web is carried betweendraw rolls 34 and 35 and subsequently wound upon the: reel 36.

Although my invention has been described as a continuous operation instep with the making of paper upon a paper machine, it is to beunderstood that the coating unit, hereinbefore described, may beoperated as a separate, independent unit.

Referring particularly to Fig. 2, it will be noted that a film 31 ofcoating material is carried upon the surface of the applicator roll 25on the entrance side of the nip formed by rolls 24 and 25. It will alsobe noted that the web 3 contacts said film as the web 3 enters the nip.If the web 3 were carried through the nip without the use of would beseparated from the surface of the roll 25 at the exit side of the nip.Inasmuch as the coating film 31, at the nip. would divide itself, aportion adhering to the web and a portion remaining on the roll surface,the separation of the web from the roll surface would be attended by apulling or stringing of the coating material, due primarily to itssurface tension. When the elastic limit of the coating material wasreached the coating film upon the web would be marked with ridges ortracks, as would-also the coating material remaining on the rollsurface.

However, by employing the member It, the sharp edge It thereof stripssubstantially all of the coating from the roll 25 before the web beginsto separate from the surface of the coating roll, in effectsimultaneously stripping the web and coating material from the surfaceof the roll 25 and affecting a comparatively clean and abrupt separationof the web from the coating roll. In this manner the pulling orstringing of the coating material iseliminated and hence streaks ortracks are prevented from forming.

It is of advantage, in roll coating, to use a coating material having ashigh a solids content as possible, preferably a coating having over 50percent solids, since subsequent drying of the coating is therebyfacilitated. It is also of advantage to apply as heavy a. coating on aweb in a single operation as possible. With my invention both of theseadvantages are attainable since the application of the coating materialto the web is not dependent only upon the amount of coating which willadhere to the web by absorption, but an additional amount ismechanically lifted from the coating roll and applied 'to the websurface.

In addition, by the peculiar formation of the curved surface l8, thatis, the surface 3 has a radius of curvature approximating the radius ofcurvature of roll 24 and substantially concentric with said roll, asmoothing operation is performed upon the coating on the web. Thisoperation is not intended to remove streaks or tracks incident to theapplication of the coating material since the edge 16 eliminates thesedisfigurations. However, unevenness in the surface of the paper itselfor protruding fibres will cause a disfigured coating, but by thesmoothing action of the curved surface these disfigurations are removed.

It will be noted that the coating upon the web 3 is brought into contactwith the smoothing surface I 8 immediately after its application to theweb surface and before the fibrous web has had time to absorb anappreciable quantity of the liquid content of the coating. In otherwords, the coating is still in -a desirably fluid state wherebysmoothing may be accomplished most effectively. This factor is alsoconducive to the use of a coating material having a relatively highsolids to liquid ratio.

While my invention is particularly suited to the coating of paper webswith mineral coating, it can be adapted to the application ofsubstantially any surface modifying liquid material wherein theseparation of the filmed surface from the applicator surface can beperformed with advantage by mechanically cutting the bond between thefilm and the applicator surface without disturbance to the surface towhich the film is applied.

I claim as my invention:

1. A device for coating paper which comprises, a rotating coating roll,means for continuously applying a coating material to the surface ofsaid roll, a rotating bed roll in substantially osculating relationshipwith said coating roll, said rolls rotating in opposite angulardirections. means for passing a web of paper into the nip of said rollsin the direction of rotation of said roll surfaces whereby a portion ofthe coating material carried upon the coating roll is transferred to asurface of the web, means for supporting said web upon said bed roll, acoating stripping blade position adjacent the exit side of said nip,said blade having an edge in contact with said coating roll to stripcoating material from said coating material and apply the same to saidweb, and means carried by said stripping blade for smoothing saidcoating on said web while the same is supported upon said bed roll.

2. A device for coating paper which comprises, a rotating coating roll,means for continuously applying a coating material to the surface ofsaid roll, a rotating bed roll in substantially osculating relationshipwith said coating roll, said rolls rotating in opposite angulardirections. means for passing a web of paper into the nip of said rollsin the direction of rotation of said roll surfaces whereby a portion ofthe coating material carried upon the coating roll is transferred to asurface of the web, means for supporting said web upon said bed roll, acoating stripping blade positioned adjacent the exit side of said nip,said blade having an edge in contact with said coating roll to stripcoating material from said coating material and apply the same to saidweb. and means carried by saidstripping blad for smoothing said coatingon said web while the same is supported upon said bed roll, said meanshaving a curved base substantially concentric with said bed roll betweenwhich and the bed roll said web passes.

GERALD D. MUGGLETON.

